My ECM Fuse blows everytime when I start the engine after a short stop, like when filling up the gas tank or starting it within 15 minutes after turning the enging off. If I wait 40 minutes or more when the engine cools off, it starts.

Sounds like something is heating up and grounding a power circuit to your ECM. There have been some issues with the Dash wiring harness in the GM trucks. I checked the bulletins for harness problems and there are several, but nothing that says there is a magic bullet for any particular problem, other than they have issues with their wring looms.
here is a link to an online repair manual site, where you can obtain the wiring diagrams for your Van. What I would do is trace all the power sources, in the wiring diagrams for that ECM fuse circuit, there must be something that heats up and allows a hot circuit to touch ground. it could even be an internal circuit to the ECM Do you have any after market electrical devices? That may be a key to your problem, as well.
http://bit.ly/mitchell_repair_manuals_online